In some cases, myalgic encephalomyelitis/chronic fatigue syndrome (for simplicity CFS) exists concurrently with fibromyalgia (FM). Some have argued that this overlap means that each is a variant of the other ? i.e., we have termed this the ?single syndrome hypothesis.? The question of whether the illnesses are the same or different is important. If they are the same, they will have the same pathophysiological underpinnings which should lead to similar therapeutic approaches. If they are found to be different, that would mean that the causes of each differs as would any attempt to develop new treatments. We have approached this question empirically and have done a number of experiments, reviewed in this proposal, which note major physiological differences between the two illnesses. One of these is in sleep architecture using an approach that counts every transition from one sleep stage to each of the others. That analysis found that patients with CFS+FM have evidence of sleep disruption not seen in patients with CFS only; specifically CFS+FM have shorter duration bouts of N2 sleep and higher probabilities of transitions from slow-wave sleep (N3) to the lightest sleep (N1) than CFS only. We have found a novel way to probe these sleep differences to further test the validity of the single syndrome hypothesis. That approach uses a rocking, cradle-like bed. Using such a bed in healthy subjects, Swiss researchers have reported more N2 sleep and more sleep spindles and delta power ? indicative of deeper sleep ? than when the subjects slept on a stationary bed. The major purpose of our using the R21 mechanism is to [1] determine whether these effects in healthy subjects translate to those with CFS and [2] to collect data to allow an accurate power analysis in a subsequent R01 application. Because our papers on sleep architecture and our available patient pool are on patients with either CFS only or CFS+FM, we will continue using these two groups in addition to a comparison group of healthy controls in this pilot study. We will use two 100 minute naps, done on separate afternoons and randomized to bed condition. Our hypothesis is that the rocking bed condition will allow CFS+FM patients to improve their sleep architecture and to report less sleepiness and/or fatigue over that of CFS only patients. We expect that the sleep of CFS+FM patients during the rocking bed condition will show more normal N2 sleep, thus resembling what is found in CFS only patients; in addition, the rocking bed should increase sleep spindle density and delta power in CFS+FM significantly more than will be seen in CFS only. We expect the rocking bed will exert the same effect on the CFS only patients as on the healthy controls. If this R21 produces these results, we see two immediate consequences: first, the data will support our earlier empiric studies showing that CFS only and CFS with FM are different pathophysiological illness processes and second, we will immediately prepare an R01 application for submission. That application will move from using naps to full overnight studies and will expand study groups to include a third one with FM only.